In this prospective study, 20 patients with bilateral catarct presenting for cataract surgery are randomly assigned to recieve an aspherical intraocular lens(AMO Tecnis Z9000) in one eye and a spherical intraocular lens(Alcon SA60AT Acrysof)in the other. All surgeries are performed by one experienced surgeon(Fung-Rong Hu,MD)with clear cornea small incision phacoemulsification and in-the-bag posterior chamber intraocular implantation.